1. Field of the Invention
This invention relates to level sensors and more particularly, though not solely, to continuous level sensors suitable for determining the level of liquids, such as water, in containers.
2. Background Art
Liquids such as water are often stored in containers in such a way that it is not possible to easily determine the level of liquid stored. The container may be for storing drinking water and/or for storing water for use in non-drinking applications such as toilet cisterns, oil tanks and laundry washing machines. For example, many houses and farms have large water storage containers made from concrete or heavy duty opaque plastics materials (such as rotationally moulded high density polyethylene). It is not possible to visually determine the amount of liquid in such containers. Sometimes it is necessary to climb on to such containers and to peer through an orifice to establish the level within the container. This is awkward and can be hazardous. Furthermore, the water container may be remotely located, requiring a special trip to determine its water level.
It is known to include level sensors in such containers in which wire pairs are provided at various discreet level within the tank. As the water level reaches on of the wire pairs, the wires are short circuited indicating to a controller the current water level in discreet increments. However, this method relies on the liquid having some conductivity and is subject to breakdown as it requires mechanical components such as wires to be continuously immersed in water. The discreet nature of the level reading is also a disadvantage.
Ultrasonic transducers have been used to provide an accurate non-contact level reading. Ultrasonic transducers (such as piezoelectric transducers) generate sound waves, at frequencies greater than about 20 kHz which is above the threshold for human hearing. The sound waves are reflected from the surface of the liquid and the time for the sound waves to be detected back at the transducer is determined. As the speed of the sound wave is known (and may be compensated for changes in temperature), this time provides a measure of the distance to the surface of the liquid and thence an indication of water level. This is an improvement over the previously described system but it is still necessary to transmit the output signal from the ultrasonic transducer to a controller and then on to an output device so that a user may be advised of the level. This has traditionally been achieved by running wires between the ultrasonic transducer and the controller and/or a display unit. This is prohibitively expensive in many home installations and also where the container is remotely located (such as on a farm).
In situations where electricity is scarce or unavailable, it would be an advantage if the power consumed by the system (and in particular the ultrasonic transducer) is minimised. Where batteries are used to provide electrical energy (for example, four AA-type cells), this would advantageously increase the time between battery replacements. It is also important to ensure that the ultrasonic transducer is transmitting its signals vertically, or nearly vertically, so that the return signal is received at the transducer. Unfortunately, many domestic and commercial water storage containers have sloped upper surfaces so that the transducer is not easily mountable on the upper surface of the container.
Accordingly, it is a object of the present invention to provide a level sensor system that will go at least some way towards overcoming the above disadvantages or which goes at least some way towards meeting the above desiderata or which will at least provide the public with a useful choice.
In one aspect, the invention may broadly be said to consist in a level sensor for providing an indication of liquid level in a container comprising:
an ultrasonic transducer for emitting an ultrasonic signal to the surface of the liquid and for detecting a return signal, reflected from the surface,
a controller that instructs the transducer to emit ultrasonic signals and receives an indication that a return signal has been detected, the controller comprising a timer for measuring the time period between emission of the ultrasonic signal and receipt of a return signal, the determined time period providing an indication of the liquid level, and
a radio transmitter that receives an indication of the liquid level and transmits a radio liquid level signal comprising the level indication to a remote output unit.
Preferably the level sensor comprises a reflector arranged to reflect ultrasonic signals emitted from the ultrasonic transducer, the ultrasonic transducer being oriented to emit ultrasonic signals towards the reflector.
Preferably the ultrasonic transducer comprises an emitter element, wherein the ultrasonic transducer is oriented to reduce condensation forming on the emitter element.
Preferably the ultrasonic transducer is oriented so that the emitter element faces horizontally and towards the reflector.
Preferably the reflector is a parabolic shaped reflector.
Preferably the level sensor comprises a housing, wherein the reflector is pivotably attached in or to the housing to alter the direction of a reflected ultrasonic signal emitted from the ultrasonic transducer.
In another aspect, the invention may broadly be said to consist in a level sensor adapted to be installed on, in or proximate a liquid container to sense a liquid level in the container, the level sensor comprising:
a housing adapted to be installed on, in or proximate a liquid container,
an ultrasonic transducer with an emitter element, the ultrasonic transducer being for emitting an ultrasonic signal for directing towards the surface of a liquid in the container and for detecting a return signal, reflected from the surface,
a parabolic reflector oriented to reflect a ultrasonic signal emitted from the ultrasonic transducer,
a controller that instructs the transducer to emit ultrasonic signals and receives an indication that a return signal has been detected, the controller comprising a timer for measuring the time period between emission of the ultrasonic signal and receipt of a return signal, the determined time period providing an indication of the liquid level, and
a radio transmitter that receives an indication of the liquid level and transmits a radio liquid level signal comprising the level indication to a remote output unit,
wherein the ultrasonic transducer emitter element is oriented at least partially face horizontally towards the parabolic reflector, and
wherein the parabolic reflector is pivotably attached to or in the housing to enable directing of a reflected ultrasonic signal emitted from the ultrasonic transducer towards the surface of the liquid in the liquid container, when the level sensor is installed on, in or proximate a liquid container.
In another aspect, the invention may broadly be said to consist in a level sensor system for providing an indication of liquid level in a container, comprising:
a transducer unit for mounting above the surface of the liquid and comprising:
an ultrasonic transducer for emitting an ultrasonic signal to the surface of the liquid and for detecting a return signal, reflected from the surface,
a controller that instructs the transducer to emit ultrasonic signals and receives an indication that a return signal has been detected, the controller comprising a timer for measuring the time period between emission of the ultrasonic signal and receipt of a return signal, the determined time period providing an indication of the liquid level, and
a radio transmitter that receives an indication of the liquid level and transmits a radio liquid level signal including the level indication, and
an output unit for locating remotely from the transducer unit and comprising
a radio receiver that receives the radio liquid level signal,
a controller that extracts the liquid level indication from the radio liquid level signal, and
a user output device that provides an indication to a user of the liquid level.
Preferably the transducer unit comprises a housing, the housing comprising an opening in its lower surface through which the ultrasonic signal and the return can signal pass.
Preferably, the housing is adapted to be mounted about an orifice formed in the upper surface of the liquid container to which the transducer unit is to be attached.
Preferably, the transducer unit includes a housing in which the various transducer unit components are housed, the housing including an opening in its lower surface through which the ultrasonic signal and the return signal pass.
Preferably, the housing has a lid and the transducer unit further comprising a heat shield is mounted above the lid to cover substantially the entire area of the lid.
Preferably, the heat shield is spaced from the lid so as to allow air circulation between the lid and the heat shield.
Preferably, the housing comprises a skirt, the lower surface of which forms a base adapted to contact the upper surface of a liquid container, wherein the skirt is formed from at least two pieces that are rotational relative to one another and engage along a camming surface formed in the skirt that is non-parallel to the base.
Preferably, the opening in the lower surface of the housing is surrounded by a wall adapted to be inserted within the orifice formed in a liquid container.
Preferably, the wall surrounding the opening in the housing's lower surface extends beyond the base of the base of the skirt.
Preferably, the transducer controller is programmed to occasionally obtain an indication of the liquid level in the container.
Preferably, the transducer controller is programmed to occasionally transmit the radio liquid level signal.
Preferably, an indication of the liquid level is obtained more often than the liquid level signal is transmitted.
Preferably, the indication of the liquid level is obtained by averaging a plurality of determined time periods between different ultrasonic signals and their respective return signals.
Preferably, the output unit includes user input means that, when activated by a user, causes the output unit to provide the indication of the liquid level to the user.
Preferably, once the user input means is activated by a user, the indication of the liquid level is provided to the user for only a predetermined period of time.
Preferably, power to operate the various components of the transducer unit is provided by batteries.
Preferably, the transducer controller and/or the output unit controller are operable in low and high power consumption modes wherein the controller or controllers are operated in the low power consumption mode unless it or they are obtaining an indication of the liquid level, transmitting a radio liquid level signal, receiving the radio liquid level signal or providing an indication to a user of the liquid level.
Preferably, in determining the time period between emission of the ultrasonic signal and the receipt of the return signal, the transducer controller is programmed to initially emit an ultrasonic signal with a first power and if no return signal is detected then to emit an ultrasonic signal with a second power, greater than the first power and to then detect a return signal.
Preferably, if no return signal is detected from the ultrasonic signal with the second power, then the transducer controller emits an ultrasonic signal with a third power, greater than the second power, and detects a return signal.
Preferably, the transducer controller activates the radio transmitter to transmit the radio liquid level signal at predetermined times and the output unit controller activates the radio receiver to listen for the transmitted radio liquid level signal for a defined period of time at said predetermined times.
Preferably, the predetermined times at which the transducer unit controller and the output unit controller are activated are set by pseudorandom number generators within the transducer unit and output unit respectively, wherein a sequence code is included in the radio liquid level signal transmitted by the transducer unit transmitter that is used to initialise the pseudorandom number generator in the output unit so that the two pseudorandom number generators may be synchronised.
Preferably, a liquid supply line is provided to the liquid container with liquid flow controlled by a flow control device in the liquid supply line, wherein the output unit includes means to allow a user to set an upper liquid level limit and a lower liquid level limit to the controller and a transmitter that transmits a radio level signal including the upper and lower liquid level limits under control of the output unit's controller, wherein the flow control device receives the radio liquid level signal transmitted by the transducer unit's transmitter and the radio level signal transmitted by the output unit's transmitter and controls the flow of liquid to the container via the supply line so that the liquid level is maintained between the upper and lower liquid level limits.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art
The term “comprising” as used in this specification means “consisting at least in part of”. Related terms such as “comprise” and “comprised” are to be interpreted in the same manner.
To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting